1. Field
The present disclosure relates to virtual tape libraries and in particular to managing the capacity of the underlying physical storage.
2. Background Information
One way that has been historically used to store data is with the use of a physical tape library. A physical tape library represents a collection of physical tapes (e.g., physical magnetic tapes). Often a physical tape library may include a large number, for example thousands to hundreds of thousands, of such physical tapes. A robotic arm known as a picker may be used to select the physical tapes from slots and insert them into physical tape drives under electronic control. The physical tape library may be coupled with a network and used for network data storage. Backup software applications or other software (e.g., on network coupled computers) may be configured to use such physical tape libraries.
A virtual tape library (VTL) provides an alternative to a physical tape library. A VTL appears to be a physical tape library to backup applications, or other software that utilize such a library—i.e., a VTL emulates a physical tape library. However, data for a VTL is not typically stored on physical magnetic tapes, but the VTL data is stored on one or more hard disk drive arrays, solid state storage devices, or other types of physical storage. This implementation offers an advantage over a physical tape library because that a VTL implementation does not typically rely on the mechanics (e.g., robotic arms) used for the physical tape library. Moreover, a backup application, or other software utilizing a VTL, does not need to know that physical magnetic tapes are not being used for data storage, and therefore no software changes are necessary. This advantage avoids modifying existing software applications (e.g., backup applications) and other implementation arrangements that are designed to use physical tape libraries. As a further advantage, the data stored by a backup application to a VTL may be stored as a file in a file system. As such, a VTL is generally able to take advantage of advanced file system functionalities, such as compression techniques for performing data deduplication, replication, redundancy, segmenting, and/or other file system based technologies.
As mentioned above, the virtual tape library should appear to be and/or should emulate a physical tape library so that the backup applications, or other software using the virtual tape library, do not need to know that they are not using a physical tape library. Accordingly, a VTL should generally be able to handle requests to read and write data to and from the underlying physical storage.